The present invention relates to data processing technology and further to particularly effective technology to be applied to instruction form in program control system, for example, to effective technology to be utilized in a microprocessor having instruction regarding processing of data called bit field.
In the prior art, for example, in a microprocessor such, as, MC68020 manufactured by Motorola, several sorts of instructions regarding processing of data in an area from arbitrary bit to arbitrary bit within a memory called bit field are prepared (the instruction being hereinafter referred to as "bit field instruction").
In the bit field instruction, as shown in FIG. 2A, three values, i.e., base address BAD, offset value Off from the base address, and field width WD indicating field length (bit number), are given as operand, thereby a required field within the memory is assigned, and logical operation processing such as AND operation or OR operation is performed to data in the field.
In the above-mentioned case, since the bit field is assigned in bit unit from arbitrary bit to arbitrary bit within the memory, it may spread through two or more words each being a read/write unit within the memory as shown in FIG. 2A. For example, when the field spreads through two words, in order to obtain information of all bits to constitute the bit field, two word addresses must be operated and the memory must be accessed twice. Consequently, in a microprocessor such as MC68020, during execution of the bit field instruction, confirmation is performed regarding whether the bit field spreads through two or more words based on the base address, the offset value and the field width, and then reading from the memory is performed.
However, the bit field does not always spread through two or more words but may be contained within one word as shown in FIG. 2B. In a microprocessor of the prior art, however, even in such case, confirmation is always performed regarding whether the bit field spreads over two or more words (hereinafter referred to as "boundary spreading"), and then reading is performed. Accordingly, due to the confirmation a problem exists in that the execution time of the bit field instruction becomes long although not necessary.